Micro LED Mesa Structure With Reflective Sidewalls and Carrier Isolation
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Solution Overview
Problem
Micro light emitting diodes (μ-LEDs) face challenges such as reduced light extraction efficiency due to spacing between adjacent mesas, lateral carrier spread leading to efficiency reduction, and crosstalk issues, which affect reliability and accuracy. Additionally, small LED pixels with high current density experience red-shift, lower maximum efficiency, and inhomogeneous emission due to degraded electrical injection and nonradiative recombination at unetched quantum well sidewalls.
Innovation Solution
A micro LED structure is designed with a mesa structure comprising a first semiconductor layer, a light emitting layer, and a second semiconductor layer. A sidewall protective layer and a sidewall reflective layer are added to enhance light extraction and reduce crosstalk. The top surface area of the second semiconductor layer is made greater than the other surface areas to optimize current injection and reduce current density, thereby improving quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If space is formed between adjacent micro LEDs to avoid carrier spreading, then carrier isolation is improved, but active light emitting area is reduced and light extraction efficiency decreases
Solution Approach 1:
An insulating layer is introduced as an intermediary substance between adjacent micro LED mesas. This insulating layer prevents carrier diffusion while allowing the mesas to be placed in close proximity, thereby maintaining high light extraction efficiency without compromising carrier isolation.
Solution Approach 2:
The harmful function of the spacing (blocking light) is separated from the useful function (isolating carriers). By extracting the isolation function and assigning it to the insulating layer, the spacing can be minimized or eliminated, allowing mesas to be positioned closer together for improved light extraction.
2Area of stationary object
If space between adjacent mesas is eliminated to increase active light emitting area, then light extraction efficiency is improved, but carriers spread laterally across adjacent mesas reducing light emitting efficiency
Solution Approach 1:
The insulating layer serves as a mediator that allows mesas to be positioned in close proximity (maximizing active area) while simultaneously preventing the harmful lateral spread of carriers (maintaining light emitting efficiency).
3Productivity
If small LED pixels with high current density are used to increase resolution, then device size is reduced, but red-shift and inhomogeneous emission occur due to degraded electrical injection
Solution Approach 1:
The patent applies local quality modification by introducing ion implantation regions with different resistance values in specific areas of the semiconductor layers. This creates localized regions with optimized electrical properties that improve current injection uniformity in small, high-density pixels.
Solution Approach 2:
The patent changes electrical parameters (resistance) through ion implantation to optimize current distribution. By adjusting the resistance in specific regions, the patent compensates for the degraded electrical injection that occurs in small, high-current-density pixels.
4Loss of energy
If peak external quantum efficiency is improved by optimizing quantum well sidewall area, then light extraction is improved, but current density increases causing electron leakage
Solution Approach 1:
The patent changes the resistance parameter through ion implantation to decouple the relationship between quantum well sidewall area and current density. This allows optimization of light extraction through sidewall area while maintaining controlled current density via resistance adjustment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed micro LED structure enhances light extraction efficiency, reduces crosstalk, and improves quantum efficiency by optimizing the semiconductor layer configurations and adding protective and reflective layers, leading to better performance and reliability in micro display applications.
Implementation Method 1
a sidewall reflective layer formed on the surface of the sidewall protective layer
Implementation Method 2
an ion implantation region formed around the semiconductor region, the ion implantation region having a resistance higher than a resistance of the semiconductor region
Implementation Method 3
space needs to be formed between adjacent μ-LEDs to avoid carriers in the epitaxial layers spreading from one mesa to an adjacent mesa
Implementation Method 4
a light emitting layer formed on the first semiconductor layer
Data Source
AI summary
A micro light emitting diode (LED) structure, includes a mesa structure. The mesa structure further includes a first semiconductor layer having a first conductive type, a light emitting layer formed on the first semiconductor layer, a second semiconductor layer formed on the light emitting layer, the second semiconductor layer having a second conductive type different from the first conductive type, a sidewall protective layer formed on the sidewalls of the mesa structures, and a sidewall reflective layer formed on the surface of the sidewall protective layer. The second semiconductor layer further includes a semiconductor region and an ion implantation region formed around the semiconductor region, the ion implantation region having a resistance higher than a resistance of the semiconductor region.